It is sometimes desirable for tires to have a combination of good wet skid resistance, low rolling resistance, tear strength, and good wear characteristics. Wear characteristics of a tire tread can be difficult to improve without sacrificing traction and/or rolling resistance. Sometimes, such properties depend upon dynamic viscoelastic properties of the tire tread rubber composition and the components utilized in the rubber composition.
In order to reduce the rolling resistance and to improve the tread wear characteristics of tires, rubbers or polymers having a high rebound physical property (low hysteresis) have been used for the tire tread rubber compositions. However, in order to increase the wet skid resistance of a tire tread, elastomers that have a relatively lower rebound physical property (higher hysteresis) which thereby undergo a greater energy loss, have sometimes been used for such tread rubber compositions. To achieve such relatively inconsistent viscoelastic properties for the tire tread rubber compositions, blends of various types of synthetic and natural rubber can be utilized in tire treads.
It can be desirable for synthetic rubbery polymers to exhibit relatively low levels of hysteresis (indicated by relatively higher rebound values). This can be important when elastomers are used in tire tread rubber compositions. In practice, the elastomers can be conventionally blended with sulfur curative, rubber reinforcing fillers such as, for example precipitated silica and rubber reinforcing carbon black, sulfur vulcanization accelerators, rubber antidegradants and other desired rubber chemicals and are then subsequently vulcanized, or cured, under pressure at an elevated temperature in a suitable mold. The physical properties of such cured rubber compositions can depend upon the degree to which the rubber reinforcing fillers, such as carbon black or silica, are homogeneously dispersed throughout the elastomer. In some instances, the degree of homogeneity of the dispersement of the reinforcing filler relates, at least in part, to the degree of affinity that carbon black or silica have for the rubbery polymer.
Amorphous silica reinforcement has sometimes been used in combination with rubber reinforcing carbon black to promote lower rolling resistance (e.g. better vehicular fuel economy) and to promote better traction (e.g. skid and braking resistance) for a tire tread rubber composition. However, use of such silica reinforcement filler, as compared to rubber reinforcing carbon black, can result in a decrease in wear resistance (e.g. increase in tread wear) of a tire tread rubber composition.
Thus, it can be desirable to provide coupling compounds, rubber compositions, and tires made therefrom to overcome the above-described issues as well as others.